Spark plug



F. KRAEMER.

SPARK PLUG.

APPLICATION FILED AUG.25. 19m.

1,427,431, Patented Au 29, 1922.

INVENTEIR F/PA/Wr Mm [Mm i iEIRNE:

UNITED STATES PATENT OFFICE.

SPARK PLUG.

Application filed August25, 1919.

To all whom it may concern:

Be it known that I, FRANK KRAEMER, a citizen of the United States, and resident of Milwaukee, in the county of Milwaukee and State of Wisconsin, have invented certain new and useful Improvements in Spark Plugs; and I do hereby declare that the following is a full, clear, and exact description thereof.

My invention relates to new and useful improvements in spark plugs for the cylinders of internal combustion engines.

It is primarily the object of my invention to provide a plug wherein is prevented the possibility of short-circuiting due to accumulations of carbon on the plug surfaces which are exposed within the engine cylinders.

Such short-circuiting, and the consequent partial or complete loss of efiiciency in spark plugs of the types heretofore provided, is caused by a film of carbon precipitated from the combustion charge of the cylinder, which accumulates on the, inner end of the insulating body of the .plug, and thus conducts the current across the surface of the insulating body and prevents it from reaching the sparking points.

It is therefore more particularly the object of my invention to protect the inner end surface of the insulating body of my plug bycreating a continuous sparking area between said end surface and the interior of the engine cylinder, and otherwise closing off said surface from the cylinder interior.

It is further my object to,provide for the disposal of carbon. precipitated adjacent the sparking portions of the plug by providing an annular negative electrode surrounded by a pocket whereby the carbon will be impelled toward and accumulate in said pocket by reason of the fact that carbon in the path of an electric spark will be projected toward the negative electrode.

A still further object resides in the provision of a plug embodying the afore cited features, which comprises a minimum number of readily assembled and simple parts, whereby to provide a strong and durable plug structure which may be economically manufactured.

With the aboveand other objects and advantages in view, my invention resides" more particularly in the novel combination, formaion and arrangement of parts herein- Specification of Letters Patent.

Patented Aug. 29, 1922. Serial No. 319,823.

after described and pended claims.

In the accompanying drawings:

Figure l is a side elevation of a spark plug embodying my invention.

Figure 2 is a longitudinal sectional View through the plug.

Figure 3 is an end view of the plug.

Referring now more articularly to the drawings, my improve spark plug comprises an outer shell or casing having its intermediate portion threaded at 5 to engage the usual threaded bore of the engine cylinder, one end portion 7 of the casing being enlarged to carry wrench faces, while the other end portion 6 is adapted to extend a slight distance into the engine cylinder and forms an outer pocket wall as will be later explained. The casing is counterbored from its outer end to form an intermediate annular shoulder 8 therein.

I provide the negative electrode of the plug in the form of a sleeve 9 which has one end portion equal in diameter to the bore of the casing, and provided with an annular outstanding flange 9 engaging the shoulder 8 of the casing. The other end portion of the sleeve, and its intermediate portion are taperingly reduced on the outer periphery to define a tapering annular pocket between the electrode sleeve and the casing portion 6, and to. provide a relatively thin sparking end for the electrode sleeve.

The cylindrical insulating body 10 of the plug has its inner end portion disposed. in

pointed out in the apthe counterbore of the casing and abuts the base end of the electrode sleeve 9, said sleeve and insulating body being provided with interfitting angular faces to prevent leakage of pressure gases through the plug. The insulating body is provided with an annular shoulder 11 adjacent its inner end, which seats a metallic washer 12 engaged by a follower sleeve 13 threaded in the outer end 6 of the casing. The body 10 may be of an material which possesses sufiicient heat an conduction resisting qualities. The stem 14 .is extended longitudinally through the insulating body and is preferably integrally" connected with an enlarged cylindrical positive electrode member 15 which extends through the negative electrode sleeve 9 and terminates in a rounded sparking head 16 having a slightly greater diameter than the diameter of the shank, whereby its periphery is in sparking relation to the outer end of the negative electrode sleeve, to thus define an annular sparking zone which insures an adequate and full spark upon passage of electric current through the plug. Nuts 17 are threaded on the outer end of the stem for the securement of the usual positive conducting wire. The diameter of the shank of the .positive electrode is approximately a quarter of an inch and thus a fairly restricted annular space is formed within the spark plug, the width of said space being however sufiicient to prevent the spark from jumping thereacross, and this annular space is continued into the insulating body 10 by countersinking its inner end at 18, the wall of said countersink being spaced from the shank of the positive electrode, and sharp edges are formed at the ends of this countersink portion to discourage creeping or capillary movement of oil or carbon thereover, the base portion of the negative electrode sleeve being also countersunk to present further angular obstacle to creeping movement of oil or carbon inwardly on the wall of the annular space in the plug. It is noted that the countersunk space 18 of the insulating body extends to the outward limit of the metal structure of the plug, the end of said countersunk space being hence approximately coincident with the outer end of the follower sleeve 13, which is threaded in the metallic casing body. Hence, any direct line drawn from the metallic outer portion of the plug to the inner electrode member 15 will pass through an air space, hence eliminating the possibility of occurrence of any current conducting fissures within that portion of the insulating body which is disposed within the confines of the casing portion of the plug, and which would hence be subjected to the greatest heat. That portion of the insulating body which carries the inner electrode member is disposed outwardly of the casing structure, and hence receives a comparatively slight amount of heat whereby to prevent the possibility of occurrence therein of fissures or cracks extending from the surface of the inner electrode member.

Enterin now into the operating advantages of t e plug, it is noted that the inner end of the insulating body 10 is disposed approximately'midway in the outer shell or casing of the plug, and that the space between this end of the insulating body and the inner end of the casing is occupied by theelectrode structure in such manner as to leave only a narrow elongated space. It is further noted that this space terminates at the inner end of the plug in an annular sparking zone which is defined by a pair of continuous concentric circular sparking edges, and I utilize this annular; sparking zone as a means of discouraging the entrance of oil or carbon into the plug,'such oil or carbon having a tendency to creep by capillary action from the exterior wall of the plug casing and then inwardly on the inner surface of the casing. Carbon in the path of an electric spark will be impelled toward the negative electrode, thus, as the sparking action of my plug occurs in the operation of the engine, oil and carbon ac cumulating at the annular edge of the negative electrode will be driven away therefrom on the outer surface of the negative electrode sleeve and will accumulate in the annular pocket provided between said sleeve and the inner end portion of the shell or casing 5, thus preventing the occurrence of an exposed free carbon deposit in the engine cylinder.

Another important advantage of my structure resides in the fact that the annular elongated space between the spark plug forms a dead gas pocket between the insulating body surface and the interior of the cylinder. Thus, the successive combustion charges for the cylinder will be prevented from. possible contact with. the insulating body to deposit carbon thereon, by the inert positioning of this dead gas pocket. The flow of combustion charges in the cylinder incidental to introduction. and compression thereof is prevented from disturbing the dead gas in the pocket by the restricted mouth of the pocket due to the sparking head 16, and by the rounded shape of this head 16 which would tend to deflect any currents of the combustion charge.

A further important advantage of my structure resides in the fact that the positive electrode 15 and the surrounding walls of the plug structure are of suflicient thickness to store and maintain a degree of heat, not sufficient to cause preignition of the charge, but which is effective within the restricted annular place of the plug to burn out carbon deposits which might possibly creep within said space.

A still further important advantage in my plug resides in the counterboring of the insu ating body at 18 to further increase the distance which oil or carbon deposits would have to creep from the inner end of the plug before establishing the electrical contact between the positive and negative electrodes, and attention is again directed to the annular edges afiorded by the various counterbores of the annular space to discourage creeping of oil or carbon.

.From the foregoing it will be seen that I provide a plurality of conditions which inhibit short circuiting accumulation of carbon at the inner end of the insulating" body of the plug, these various conditions possessing their maximum individual efliciencies to combat the different tendencies of accumulation of carbon which occur in the use of a spark plug. Practice has demonstrated that, that by reason of the co-action of these various conditions in my plug, it is practically impossible to-procure a short circuiting accumulation of carbon in the plug, even upon severe and continued maladjustments of the fuel and oil supply of the engine. Oil and carbon tend to accumulate on and in the spark plug particularly after the engine has ceased operation, and my improved plug is to a large extent selfcleaning by reason of the burning out action effected in the restricted annular space of the plug, and by reason of the shedding action on the carbon exerted by passage of sparks across the annular sparking zone, and the remote positioning of the inner end of the insulating body prevents reduction of the efliciency of the spark plug upon starting up the operation of the engine and prior to completion of this self-cleansing action. I am aware that spark plugs have heretofore been provided including an annular negative electrode member surrounding the positive electrode, but in such plugs sparking points are provided about the negative electrode which define pockets therebetween, said pockets being out of the sparking zone and thus permitting oil and carbon to creep therethrough into the interior of the plug.

While I have shown and described a preferred embodiment of my invention, it will be appreciated that various changes and modifications of structure may be employed to meet differing conditions of use and manufacture, or that various carbon-preventing phases of the plug may be used independently without departing in any manner from the spirit of my invention.

What is claimed is:

1. A spark plug comprising a centrally bored metallic casing, an insulating body secured in said casing and having a counterbore in the inner end thereof extending substantially the length of the casing and a central bore in the outer end of the body communicating with said counterbore, a tubular electrode secured within said casing and having its outer end projected therefrom and its inner end counterbored to substantially form a continuation of the counterbore in said insulating body, and a second electrode positioned within said insulating body and extended through said tubular electrode with its inner end terminating adjacent the outer end thereof and spaced therefrom to define a spark gap.

2. A spark plug, comprising a centrally bored metallic casing, the upper portion thereof being counter boredto provide an intermediate shoulder, a tubular electrode having its upper end flanged for engagement with the intermediate shoulder of said casing and having its other end projected beyond the inner end of said casing, an insulating body extended into the counter bored portion of said casing and having a part adapted to abut the flange of saidvelectrode ,to confine the same between it and said casing shoulder, said body having a central opening communicating with a counter-sunk recess in the inner portion thereof which extends throughout the entire portion thereof confined within said casing, means "for securing said insulating body in said casing whereby the flange of said 'electrode will be held firm against said casing shoulder, tha upper end of said electrode being counter bored whereby a continuation of the counter bored recess of said insulating body will be provided a second electrode passed through said first mentionedelectrode and insulatin body and having its inner end terminating adjacent the inner end of Said first mentioned electrode to provide a spark gap, and its outer end exteriorlyof the insulating body and providing a terminal.

In testimony that I claim the foregoing, I have hereunto set my hand at Milwaukee, in the county of Milwaukee and State of Wisconsin.

FRANK KRAEMER. 

